The present invention relates to a videocassette recorder for reproducing a video signal recorded by more than one broadcasting system, and more particularly, to a circuit for discriminating the recording broadcasting system of a video signal recorded on a video tape, and to a method for reproducing a chrominance signal by using the circuit.
The VHS recording system is characterized in that there is no interval, i.e., guard band, between the tracks where a video signal is recorded, which, though enabling high-density recording, tends to generate inter-track crosstalk in a system. Therefore, to reduce the effects of crosstalk, such a system employs an azimuth angle whose reduction effect is greater at higher frequencies. Accordingly, the luminance signal of a picture signal exhibits little crosstalk since it is recorded in a higher frequency band, while the chrominance signal, being recorded in a lower frequency band, experiences a relatively high degree of crosstalk.
To prevent the generation of the crosstalk, in a VHS type videocassette recorder, the chrominance signal is recorded while being phase-shifted every horizontal scanning line. That is, the CH-1 and CH-2 heads alternately record signals from the lower right to the upper left along a video tape.
In recording a signal by the NTSC broadcasting system, the CH-1 head records by shifting the phases of a first, second, third and fourth horizontal scanning line of a recorded signal, to 0.degree., +90.degree., +180.degree. and +270.degree., respectively. That is, the CH-1 head records the signal by shifting the phase of each horizontal scanning line by 90.degree.. Meanwhile, the CH-2 head records signals by delaying the phase by 90.degree., i.e., -90.degree., -180.degree., -270.degree. and -360.degree..
During reproduction, the phase is shifted conversely with respect to the recording operation.
In recording the signal by the PAL system, the CH-1 head does not shift the phase and the CH-2 head makes the phase lag by 90.degree. for every horizontal scanning line. During reproduction, the CH-1 head does not shift the phase and the CH-2 head makes the phase lead by 90.degree. for every horizontal scanning line.
The PAL broadcasting system includes PAL-B, PAL-C and PAL-M types. The vertical sync frequency of the PAL-B and PAL-C systems is 50 Hz, while that of the PAL-M system is 60 Hz and thus is the same as the NTSC broadcasting system.
When signals recorded in a video tape by different broadcasting system are reproduced, a reproducing mode of a tape recorder should be adjusted to corresponding to the broadcasting system of the recorded signal.
In a conventional videocassette recorder, the corresponding broadcasting system to the tape is selected by the combination of switches or, sequentially searched by using a microcomputer and a tact switch. This, however, necessitates the generation of a control signal corresponding to each broadcasting system, which complicates the hardware or encumbers a user with additional manipulation.